1. Field of the Invention
The present invention relates to a write-once recording medium (optical disk) and an information management method thereof. More particularly, the invention relates to the optical disk which has a logical format designed in a manner to reproduce information from the optical disk in a reproducing drive for a read-only optical disk (for example, CD-ROM).
2. Description of the Prior Art
A compact disk (CD) developed as a digital audio disk has a capacity to record as much data as 500 to 600 M bytes though it has a diameter of 12 cm. With the capability to record such a large quantity of data, like a magnetic disk (for example, floppy disk or harddisk), the optical disk has been used as a read-only information recording medium. The CD used as an information recording medium is referred to as CD-ROM, which are commercially available as a medium recording dictionaries or maps.
The CD-ROM has a physical property and format standardized in a CD standard manual (red book) and CD-ROM standard manual (yellow book) published by Philips Company. The physical property and format include a physical structure of the disk itself, an optical property, a signal processing system, an error correcting system, a sector number, a sector capacitance, and the like. This is de facto standard.
And, recently, a logical format (for example, management of directory files) located between the physical format and an application layer has been standardized as ISO 9660. The standardization of the logical format results in keeping commercially-available CD-ROMs compatible with each other. It is supposed that the CD-ROMs rapidly pervade as a recording medium more and more of our society.
Not only the read-only CD-ROMs but also writable optical disks have been widely developed. The writable optical disks include write-once optical disks and rewritable disks. For the former disks, information can be written once and for the latter ones, information can be written and erased many times.
The rewritable optical (magnetic) disks employ opto-magnetic effect or phase transition. Hence, they have a different physical property from that of the CDs or CD-ROMs, thereby being unable to keep both the former rewritable disks and the latter CDs and CD-ROMs compatible with each other at the current stage.
On the other hand, the write-once optical disk can manage to have a physical property to be compatible with a music CD or CD-ROM if it selectively uses a proper material because no consideration is required for erasing and rewriting. It means that if the write-once optical disk is designed to have the same physical and logical formats as the music CDs and CD-ROMs, they can be reproduced in a CD-ROM player.
As an example, the method of using a write-once disk as a music CD can be referred. This method comprises the steps of selecting some pieces of music from music data being stocked in a store as required, generating a table of contents (TOC) required for managing these pieces of music, and recording the TOC and the music data on the write-once optical disk for producing an original music CD.
As stated above, since the CD-ROM has a capacity of recording a large quantity of information, it has to manage a lot of files efficiently. For this purpose, it employs a file hierarchy structure, that is, a so-called directory hierarchy structure as well as a volume structure for managing several CD-ROMs systematically.
When all of files should be stored, in which contain information or data, are written in the write-once disk at a time, it is possible to generate hierachial directories and/or managing information for managing them in the same manner as for CD-ROM and to write in simultaneously with the files.
In this case it is possible to grasp all the file information and the directory information, to create the optimum management information in a large host computer, and to write the information based on a logical format being compatible with that of the CD-ROM. Thus, the write-once disk so written may be used interchangeably with the CD-ROM.
On the other hand, when the writing operation is carried out intermittently for adding a file or files to the previously written files, the hierachial directories have to be rewritten every time the file or files are added to the disk. Unfortunately it is impossible to rewrite the directories previously written in the write-once disk, therefore, in such a case that the files are added on, it is difficult to keep the interchangeability with the CD-ROM.